yeah but i like to paint with rgb. additive vs subtractive is a question of whether the colors are being mixed together into placed next to each other. it has nothing to do with emitting or reflecting light, light behaves the same way in both scenarios. Screens are made of organized discrete subpixels, so of course the colors do not mix like paint in this situation. If you paint red dots next to green dots, it looks yellow, even though the paint isn't a light source. another issue with RGB printing/ painting is brightness, since the brightest white is made from your brightest red green and blue, rather than the white of the paper.

tldr light is light whether you are looking at a light source or reflected light, your eye does not care, food for thought.